This invention relates to methods of producing hair follicles in vitro, compositions for producing hair follicles in vitro, in vitro produced hair follicles, methods of providing an in vitro produced hair shaft at an interfollicular or intrafollicular site, methods of treating hair loss by providing an in vitro produced hair shaft at an interfollicular or intrafollicular site and assays for studying the effect of test agents on hair biology. The invention also provides the similar methods and products which are, or use, immature follicles (“defined herein as proto-hairs”).